1. Field of the Invention
The invention relates to an electrical machine with a cooling device for the removal of waste heat, having a stator with a stator laminated core having recesses for cooling ducts which carry a cooling medium, the cooling ducts being connected by at least one return element.
2. Description of the Related Art
During the operation of an electrical machine for the conversion of electrical energy into mechanical energy or vice versa, heat losses occur. In order to protect the machine from damage, these undesirable heat losses must be removed from the machine. For this purpose, it is current practice to provide electrical machines with a cooling device in which, for example, a flowing coolant accepts the heat due to the losses and transports it away from the electrical machine to a heat exchanger. The employment of such a cooling device also permits the power of the electrical machine to be substantially increased.
In the case of electrical machines in installations which themselves generate waste heat, as in the field of automobile technology in the case of a combination with an internal combustion engine, great effort must be made to remove the waste heat. In addition, the present development of motor vehiclesxe2x80x94from the point of view of fuel saving and reduced emission with a limited amount of installation space availablexe2x80x94demands particularly efficient electrical machines, which are compact in construction and economical in weight.
DE 197 57 605 discloses an internal rotor electric motor with cooling ducts cast into the stator laminated core and extending in the axial direction. The end plates arranged at the end surfaces of the stator laminated core have penetrations, through which the axial cooling ducts are led out of the stator laminated core and connected to one another by means of tubular return elements.
In addition, EP 0 925 839 A1 describes an electric motor of internal rotor type whose casing has axial cooling ducts which are flow-connected with one another by means of return elements which can be attached to the casing and by recesses in the end plates.
The disadvantage of the two solutions mentioned, is that due to the end surface return elements, the axial installation length of the electrical machine is determined by the cooling device rather than by the electrical part.
The invention is based on the object of providing an electrical machine, with a cooling device, which has the smallest possible axial installation length.
Due to the design of the stator laminated core having return elements arranged elements according to the invention, an electrical machine can be constructed in a very compact manner. The axial installation space gained can be used for the arrangement of further functional units, for example in the strictly limited engine compartment of a motor vehicle.
In the case of an electrical machine of the external rotor type, it is particularly advantageous for the return element section extending essentially in the peripheral direction to be arranged radially on the inside relative to the stator laminated core. The concentric internal space of the stator laminated core present in the case of an external rotor can be used, without special measures, for the arrangement of the return elements.
In addition, configuring the return element within the axial extent of the stator laminated core is a particularly space-saving arrangement.
In a further advantageous embodiment, the return element connects adjacent cooling ducts in pairs. This avoids any hydraulic short-circuit.
A particularly simple variant, from the point of view of manufacturing technology, provides for a tubular return element. This can be easily pushed onto adjacent cooling ducts and connected to the latter in a manner so as to seal.
For the manufacture of the return element, it is likewise useful for the latter to be configured with a plurality of parts, i.e. with at least one channel part and at least one closing part which closes the channel part so as to seal it.
In a particularly simple embodiment, the closing part consists of a plastic. For the closing of a channel part so as to seal it, the closing part in plastic can, for example, have a press fit and be pressed into the channel part in a simple manner.
A particular advantage results if the channel part of a return element is integrally configured with the cooling ducts extending in the stator laminated core and being in flow connection with the channel part. This permits the number of parts in the cooling device to be essentially reduced and low-cost manufacture is made possible.
In a particularly advantageous manner, the channel part with the cooling ducts extending in the stator laminated core and being in flow connection with the channel part is embodied as a cast part or molded part. The cast or molded material can in this case be in particularly close contact with the contour of the stator laminated core, which arrangement effects a particularly effective removal of heat due to the cooling device when the electrical machine is in operation.
A plurality of channel parts of the return elements, arranged radially relative to the stator laminated core can advantageously be connected to one another by means of holding segments. The mechanical stability of the cooling device can be markedly improved by this measure.
In addition, it is also useful for a plurality of closure parts to be integrally configured in the form of a cover, which closes a plurality of channel parts so that they are sealed. By this means, the number of assembly steps necessary for the manufacture of the electrical machine can be reduced and an electrical machine can be manufactured in a shorter time.
The openings for the cooling ducts and connecting means in the stator laminated core are advantageously arranged on a common reference circle. When stamping the individual laminations, for example, this provides the advantage that the number of stamping patterns and tools can be kept small.
A further advantageous embodiment of the invention provides for a plurality of cooling ducts, which are separated from one another with respect to flow, to be connected in pairs by return ducts extending essentially in the peripheral direction. These return ducts are formed on a flange part on the end surface of the stator laminated core opposite to the return elements so that the cooling ducts are sealed. The return ducts in this flange part can be manufactured by milling from a solid material or by deep-drawing a sheet-metal part.
It is advantageous to configure the flange part, in a further function, as a stator support. By this means, an additional part functioning as a stator support can be omitted.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.